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<h2 id="引言："><a href="#引言：" class="headerlink" title="引言："></a>引言：</h2><blockquote>
<p>Java8中有两大最为重要的改变。一个是Lambda表达式；另一个则是Stream API。</p>
</blockquote>
<h3 id="一、Stream-API-说明"><a href="#一、Stream-API-说明" class="headerlink" title="一、Stream API 说明"></a>一、Stream API 说明</h3><ol>
<li><strong>Stream API ( java.util.stream)</strong> 把真正的<strong>函数式编程风格</strong>引入到Java中。这是目前为止对Java类库最好的补充，因为Stream API可以极大提供Java程序员的生产力，让程序员写出高效率、干净、简洁的代码。</li>
<li>Stream 是 Java8 中处理集合的关键抽象概念，它可以指定你希望对集合进行的操作，可以执行非常复杂的查找、过滤和映射数据等操作。 <strong>使用Stream API 对集合数据进行操作，就类似于使用 SQL 执行的数据库查询</strong>。也可以使用 Stream API 来并行执行操作。简言之，Stream API 提供了一种<strong>高效且易于使用的处理数据的方式</strong>。</li>
<li>实际开发中，项目中多数数据源都来自于Mysql，Oracle等。但现在数据源可以更多了，有MongDB，Radis等，而这些NoSQL的数据就需要Java层面去处理。</li>
<li>Stream 和 Collection 集合的区别：<strong>Collection 是一种静态的内存数据结构，而 Stream 是有关计算的</strong>。前者是主要面向内存，存储在内存中，后者主要是面向 CPU，通过 CPU 实现计算。</li>
<li>Stream 是数据渠道，用于操作数据源（集合、数组等）所生成的元素序列。“集合讲的是数据，Stream讲的是计算！”<blockquote>
<p>注意：</p>
<ul>
<li>Stream 自己不会存储元素</li>
<li>Stream 不会改变源对象。相反，他们会返回一个持有结果的新Stream</li>
<li>Stream 操作是延迟执行的。这意味着他们会等到需要结果的时候才执行</li>
</ul>
</blockquote>
</li>
</ol>
<h3 id="二、Stream-操作步骤"><a href="#二、Stream-操作步骤" class="headerlink" title="二、Stream 操作步骤"></a>二、Stream 操作步骤</h3><ol>
<li>创建 Stream<blockquote>
<p>一个数据源（如：集合，数组），获取一个流</p>
</blockquote>
</li>
<li>中间操作<blockquote>
<p>一个中间操作链，对数据源的数据进行处理</p>
</blockquote>
</li>
<li>终止操作<blockquote>
<p>一旦执行终止操作，<strong>就执行中间操作链</strong>，并产生结果。之后，不会再被利用</p>
</blockquote>
</li>
</ol>
<h3 id="三、创建-Stream"><a href="#三、创建-Stream" class="headerlink" title="三、创建 Stream"></a>三、创建 Stream</h3><h4 id="1、通过集合"><a href="#1、通过集合" class="headerlink" title="1、通过集合"></a>1、通过集合</h4><p>Java8 中的 Collection 接口被扩展，提供了两个获取流的方法：</p>
<blockquote>
<ul>
<li><strong>default Stream&lt;E&gt; stream()：</strong>返回一个顺序流</li>
<li><strong>default Stream&lt;E&gt; parallelStream()：</strong>返回一个并行流</li>
</ul>
</blockquote>
<h4 id="2、通过数组"><a href="#2、通过数组" class="headerlink" title="2、通过数组"></a>2、通过数组</h4><p>Java8 中的 Arrays 的静态方法 stream() 可以获取数组流：</p>
<blockquote>
<ul>
<li><strong>static &lt;T&gt; Stream&lt;T&gt; stream(T[] array)：</strong>返回一个流</li>
</ul>
<p>重载形式，能够处理对应基本类型的数组：</p>
<blockquote>
<ul>
<li><strong>public static IntStream stream(int[] array)</strong></li>
<li><strong>public static LongStream stream(long[] array)</strong></li>
<li><strong>public static DoubleStream stream(double[] array)</strong></li>
</ul>
</blockquote>
</blockquote>
<h4 id="3、通过Stream的of"><a href="#3、通过Stream的of" class="headerlink" title="3、通过Stream的of"></a>3、通过Stream的of</h4><p>可以调用Stream类静态方法 of(), 通过显示值创建一个流。它可以接收任意数量的参数。</p>
<blockquote>
<ul>
<li><strong>public static&lt;T&gt; Stream&lt;T&gt; of(T… values)：</strong>返回一个流</li>
</ul>
</blockquote>
<h4 id="4、创建无限流"><a href="#4、创建无限流" class="headerlink" title="4、创建无限流"></a>4、创建无限流</h4><p>可以使用静态方法 Stream.iterate() 和 Stream.generate(),创建无限流。</p>
<blockquote>
<p>迭代：</p>
<blockquote>
<p><strong>public static&lt;T&gt; Stream&lt;T&gt; iterate(final T seed, final UnaryOperator&lt;T&gt; f)</strong></p>
</blockquote>
<p>生成：</p>
<blockquote>
<p><strong>public static&lt;T&gt; Stream&lt;T&gt; generate(Supplier&lt;T&gt; s)</strong></p>
</blockquote>
</blockquote>
<pre class="language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Employee</span> <span class="token punctuation">&#123;</span>

	<span class="token keyword">private</span> <span class="token keyword">int</span> id<span class="token punctuation">;</span>
	<span class="token keyword">private</span> <span class="token class-name">String</span> name<span class="token punctuation">;</span>
	<span class="token keyword">private</span> <span class="token keyword">int</span> age<span class="token punctuation">;</span>
	<span class="token keyword">private</span> <span class="token keyword">double</span> salary<span class="token punctuation">;</span>

	<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">getId</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">return</span> id<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setId</span><span class="token punctuation">(</span><span class="token keyword">int</span> id<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>id <span class="token operator">=</span> id<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token class-name">String</span> <span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">return</span> name<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setName</span><span class="token punctuation">(</span><span class="token class-name">String</span> name<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">getAge</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">return</span> age<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setAge</span><span class="token punctuation">(</span><span class="token keyword">int</span> age<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token keyword">double</span> <span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">return</span> salary<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">setSalary</span><span class="token punctuation">(</span><span class="token keyword">double</span> salary<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>salary <span class="token operator">=</span> salary<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Employee()....."</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token keyword">int</span> id<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>id <span class="token operator">=</span> id<span class="token punctuation">;</span>
		<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Employee(int id)....."</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token keyword">int</span> id<span class="token punctuation">,</span> <span class="token class-name">String</span> name<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>id <span class="token operator">=</span> id<span class="token punctuation">;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token keyword">public</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token keyword">int</span> id<span class="token punctuation">,</span> <span class="token class-name">String</span> name<span class="token punctuation">,</span> <span class="token keyword">int</span> age<span class="token punctuation">,</span> <span class="token keyword">double</span> salary<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>

		<span class="token keyword">this</span><span class="token punctuation">.</span>id <span class="token operator">=</span> id<span class="token punctuation">;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>name <span class="token operator">=</span> name<span class="token punctuation">;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>age <span class="token operator">=</span> age<span class="token punctuation">;</span>
		<span class="token keyword">this</span><span class="token punctuation">.</span>salary <span class="token operator">=</span> salary<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token annotation punctuation">@Override</span>
	<span class="token keyword">public</span> <span class="token class-name">String</span> <span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">return</span> <span class="token string">"Employee&#123;"</span> <span class="token operator">+</span> <span class="token string">"id="</span> <span class="token operator">+</span> id <span class="token operator">+</span> <span class="token string">", name='"</span> <span class="token operator">+</span> name <span class="token operator">+</span> <span class="token char">'\''</span> <span class="token operator">+</span> <span class="token string">", age="</span> <span class="token operator">+</span> age <span class="token operator">+</span> <span class="token string">", salary="</span> <span class="token operator">+</span> salary <span class="token operator">+</span> <span class="token char">'&#125;'</span><span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token annotation punctuation">@Override</span>
	<span class="token keyword">public</span> <span class="token keyword">boolean</span> <span class="token function">equals</span><span class="token punctuation">(</span><span class="token class-name">Object</span> o<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">this</span> <span class="token operator">==</span> o<span class="token punctuation">)</span>
			<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
		<span class="token keyword">if</span> <span class="token punctuation">(</span>o <span class="token operator">==</span> <span class="token keyword">null</span> <span class="token operator">||</span> <span class="token function">getClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">!=</span> o<span class="token punctuation">.</span><span class="token function">getClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
			<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>

		<span class="token class-name">Employee</span> employee <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">Employee</span><span class="token punctuation">)</span> o<span class="token punctuation">;</span>

		<span class="token keyword">if</span> <span class="token punctuation">(</span>id <span class="token operator">!=</span> employee<span class="token punctuation">.</span>id<span class="token punctuation">)</span>
			<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
		<span class="token keyword">if</span> <span class="token punctuation">(</span>age <span class="token operator">!=</span> employee<span class="token punctuation">.</span>age<span class="token punctuation">)</span>
			<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
		<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token class-name">Double</span><span class="token punctuation">.</span><span class="token function">compare</span><span class="token punctuation">(</span>employee<span class="token punctuation">.</span>salary<span class="token punctuation">,</span> salary<span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token number">0</span><span class="token punctuation">)</span>
			<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
		<span class="token keyword">return</span> name <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token operator">?</span> name<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span>employee<span class="token punctuation">.</span>name<span class="token punctuation">)</span> <span class="token operator">:</span> employee<span class="token punctuation">.</span>name <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>

	<span class="token annotation punctuation">@Override</span>
	<span class="token keyword">public</span> <span class="token keyword">int</span> <span class="token function">hashCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
		<span class="token keyword">int</span> result<span class="token punctuation">;</span>
		<span class="token keyword">long</span> temp<span class="token punctuation">;</span>
		result <span class="token operator">=</span> id<span class="token punctuation">;</span>
		result <span class="token operator">=</span> <span class="token number">31</span> <span class="token operator">*</span> result <span class="token operator">+</span> <span class="token punctuation">(</span>name <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token operator">?</span> name<span class="token punctuation">.</span><span class="token function">hashCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">:</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		result <span class="token operator">=</span> <span class="token number">31</span> <span class="token operator">*</span> result <span class="token operator">+</span> age<span class="token punctuation">;</span>
		temp <span class="token operator">=</span> <span class="token class-name">Double</span><span class="token punctuation">.</span><span class="token function">doubleToLongBits</span><span class="token punctuation">(</span>salary<span class="token punctuation">)</span><span class="token punctuation">;</span>
		result <span class="token operator">=</span> <span class="token number">31</span> <span class="token operator">*</span> result <span class="token operator">+</span> <span class="token punctuation">(</span><span class="token keyword">int</span><span class="token punctuation">)</span> <span class="token punctuation">(</span>temp <span class="token operator">^</span> <span class="token punctuation">(</span>temp <span class="token operator">>>></span> <span class="token number">32</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token keyword">return</span> result<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span>

<span class="token keyword">class</span> <span class="token class-name">EmployeeData</span> <span class="token punctuation">&#123;</span>
	<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> <span class="token function">getEmployees</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
		<span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1001</span><span class="token punctuation">,</span> <span class="token string">"马化腾"</span><span class="token punctuation">,</span> <span class="token number">34</span><span class="token punctuation">,</span> <span class="token number">6000.38</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1002</span><span class="token punctuation">,</span> <span class="token string">"马云"</span><span class="token punctuation">,</span> <span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">9876.12</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1003</span><span class="token punctuation">,</span> <span class="token string">"刘强东"</span><span class="token punctuation">,</span> <span class="token number">33</span><span class="token punctuation">,</span> <span class="token number">3000.82</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1004</span><span class="token punctuation">,</span> <span class="token string">"雷军"</span><span class="token punctuation">,</span> <span class="token number">26</span><span class="token punctuation">,</span> <span class="token number">7657.37</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1005</span><span class="token punctuation">,</span> <span class="token string">"李彦宏"</span><span class="token punctuation">,</span> <span class="token number">65</span><span class="token punctuation">,</span> <span class="token number">5555.32</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1006</span><span class="token punctuation">,</span> <span class="token string">"比尔盖茨"</span><span class="token punctuation">,</span> <span class="token number">42</span><span class="token punctuation">,</span> <span class="token number">9500.43</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1007</span><span class="token punctuation">,</span> <span class="token string">"任正非"</span><span class="token punctuation">,</span> <span class="token number">26</span><span class="token punctuation">,</span> <span class="token number">4333.32</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1008</span><span class="token punctuation">,</span> <span class="token string">"扎克伯格"</span><span class="token punctuation">,</span> <span class="token number">35</span><span class="token punctuation">,</span> <span class="token number">2500.32</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
		<span class="token keyword">return</span> list<span class="token punctuation">;</span>
	<span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span></code></pre>

<pre class="language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">StreamAPITest</span> <span class="token punctuation">&#123;</span>
    <span class="token comment">/* 创建Stream方式一：通过集合 */</span>
    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test1</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employees <span class="token operator">=</span> <span class="token class-name">EmployeeData</span><span class="token punctuation">.</span><span class="token function">getEmployees</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">//default Stream&lt;E> stream(): 返回一个顺序流</span>
        <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> stream <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">//default Stream&lt;E> parallelStream(): 返回一个并行流</span>
        <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> pa <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">parallelStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>

    <span class="token comment">/* 创建Stream方式二：通过数组 */</span>
    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test2</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span> arr1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">int</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">&#123;</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">&#125;</span><span class="token punctuation">;</span>
        <span class="token comment">//调用Arrays类的static &lt;T> Stream&lt;T> stream(T[] array): 返回一个流</span>
        <span class="token class-name">IntStream</span> stream1 <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span>arr1<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token class-name">Employee</span> e1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1001</span><span class="token punctuation">,</span> <span class="token string">"Tom"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">Employee</span> e2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1002</span><span class="token punctuation">,</span> <span class="token string">"Jerry"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">Employee</span><span class="token punctuation">[</span><span class="token punctuation">]</span> arr2 <span class="token operator">=</span> <span class="token punctuation">&#123;</span>e1<span class="token punctuation">,</span> e2<span class="token punctuation">&#125;</span><span class="token punctuation">;</span>
        <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> stream2 <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span>arr2<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>

    <span class="token comment">/* 创建Stream方式三：通过Stream的of() */</span>
    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test3</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> stream <span class="token operator">=</span> <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>

    <span class="token comment">/* 创建Stream方式四：通过无限流 */</span>
    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test4</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token comment">/** 迭代
         * public static&lt;T> Stream&lt;T> iterate(final T seed, final UnaryOperator&lt;T> f)
         */</span>
        <span class="token comment">//遍历前10个偶数</span>
        <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">iterate</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> t <span class="token operator">-></span> t <span class="token operator">+</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">limit</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span>i <span class="token operator">-></span> <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">iterate</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> t <span class="token operator">-></span> t <span class="token operator">+</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">limit</span><span class="token punctuation">(</span><span class="token number">12</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">/** 生成
         * public static&lt;T> Stream&lt;T> generate(Supplier&lt;T> s)
         */</span>
        <span class="token class-name">Stream</span><span class="token punctuation">.</span><span class="token function">generate</span><span class="token punctuation">(</span><span class="token class-name">Math</span><span class="token operator">::</span><span class="token function">random</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">limit</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span></code></pre>

<h3 id="四、Stream-的中间操作"><a href="#四、Stream-的中间操作" class="headerlink" title="四、Stream 的中间操作"></a>四、Stream 的中间操作</h3><p>  多个<strong>中间操作</strong>可以连接起来形成一个<strong>流水线</strong>，除非流水线上触发终止操作，否则<strong>中间操作不会执行任何的处理</strong>！而在终止操作时一次性全部处理，称为<strong>“惰性求值”</strong>。</p>
<h4 id="1、筛选与切片"><a href="#1、筛选与切片" class="headerlink" title="1、筛选与切片"></a>1、筛选与切片</h4><table>
<thead>
<tr>
<th>方法</th>
<th>描述</th>
</tr>
</thead>
<tbody><tr>
<td><strong>filter</strong>(Predicate p)</td>
<td>接受 Lambda，从流中排出某些元素</td>
</tr>
<tr>
<td><strong>distinct</strong>()</td>
<td>筛选，通过流所生成元素的 hashCode() 和 equals() 去除重复元素</td>
</tr>
<tr>
<td><strong>limit</strong>(long maxSize)</td>
<td>截断流，使其元素不超过给定数量</td>
</tr>
<tr>
<td><strong>skip</strong>(long n)</td>
<td>跳过元素，返回一个扔掉了前 n 个元素的流。若流中元素不足 n 个，则返回一个空流。与 limit(n) 互补</td>
</tr>
</tbody></table>
<pre class="language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test1</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token class-name">EmployeeData</span><span class="token punctuation">.</span><span class="token function">getEmployees</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token comment">// filter(Predicate p) —— 接收 Lambda，从流中排除某些元素。</span>
    <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> stream <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    stream<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>e <span class="token operator">-></span> e<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">7000</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token comment">// limit(n) —— 截断流，使其元素不超过给定数量。</span>
    list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">limit</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span>e <span class="token operator">-></span> <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>e<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token comment">// skip(n) —— 跳过元素，返回一个扔掉了前 n 个元素的流。若流中元素不足 n 个，则返回一个空流。与 limit(n) 互补</span>
    list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">skip</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token comment">// distinct() —— 筛选，通过流所生成元素的 hashCode() 和 equals() 去除重复元素</span>
    list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1010</span><span class="token punctuation">,</span><span class="token string">"刘强东"</span><span class="token punctuation">,</span><span class="token number">40</span><span class="token punctuation">,</span><span class="token number">8000</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1010</span><span class="token punctuation">,</span><span class="token string">"刘强东"</span><span class="token punctuation">,</span><span class="token number">41</span><span class="token punctuation">,</span><span class="token number">8000</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Employee</span><span class="token punctuation">(</span><span class="token number">1010</span><span class="token punctuation">,</span><span class="token string">"刘强东"</span><span class="token punctuation">,</span><span class="token number">40</span><span class="token punctuation">,</span><span class="token number">8000</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">distinct</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span></code></pre>

<h4 id="2、映射"><a href="#2、映射" class="headerlink" title="2、映射"></a>2、映射</h4><table>
<thead>
<tr>
<th>方法</th>
<th>描述</th>
</tr>
</thead>
<tbody><tr>
<td><strong>map</strong>(Function&lt;T, R&gt; f)</td>
<td>接收一个函数作为参数，该函数会被应用到每个元素上，并将其映射成一个新的R类型的元素，形成一个新的流Stream&lt;R&gt;。</td>
</tr>
<tr>
<td><strong>mapToInt</strong>(ToIntFunction&lt;T&gt; f)</td>
<td>接收一个函数作为参数，该函数会被应用到每个元素上，并将其映射成一个新的int元素，产生一个新的 IntStream。</td>
</tr>
<tr>
<td><strong>mapToLong</strong>(ToLongFunction&lt;T&gt; f)</td>
<td>接收一个函数作为参数，该函数会被应用到每个元素上，并将其映射成一个新的long元素，产生一个新的 LongStream。</td>
</tr>
<tr>
<td><strong>mapToDouble</strong>(ToDoubleFunction&lt;T&gt; f)</td>
<td>接收一个函数作为参数，该函数会被应用到每个元素上，并将其映射成一个新的double元素，产生一个新的 DoubleStream。</td>
</tr>
<tr>
<td><strong>flatMap</strong>(Function&lt;T, Stream&lt;R&gt;&gt; f)</td>
<td>接收一个函数作为参数，将流中的每个值都换成另一个流Stream&lt;R&gt;，然后把所有流连接成一个流Stream&lt;R&gt;。</td>
</tr>
<tr>
<td><strong>flatMapToInt</strong>(Function&lt;T, IntStream&gt; f)</td>
<td>接收一个函数作为参数，将流中的每个值都换成另一个IntStream，然后把所有IntStream连成一个IntStream。</td>
</tr>
<tr>
<td><strong>flatMapToLong</strong>(Function&lt;T, LongStream&gt; f)</td>
<td>接收一个函数作为参数，将流中的每个值都换成另一个LongStream，然后把所有LongStream连成一个LongStream。</td>
</tr>
<tr>
<td><strong>flatMapToDouble</strong>(Function&lt;T, DoublStream&gt; f)</td>
<td>接收一个函数作为参数，将流中的每个值都换成另一个DoublStream，然后把所有DoublStream连成一个DoublStream。</td>
</tr>
</tbody></table>
<pre class="language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">StreamAPITest</span> <span class="token punctuation">&#123;</span>
    <span class="token annotation punctuation">@Test</span> <span class="token comment">/* 映射 */</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test2</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token comment">// map(Function f) —— 接收一个函数作为参数，将元素转换成其他形式或提取信息，该函数会被应用到每个元素上，并将其映射成一个新的元素。</span>
        <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">asList</span><span class="token punctuation">(</span><span class="token string">"aa"</span><span class="token punctuation">,</span> <span class="token string">"bb"</span><span class="token punctuation">,</span> <span class="token string">"cc"</span><span class="token punctuation">,</span> <span class="token string">"dd"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span>str <span class="token operator">-></span> str<span class="token punctuation">.</span><span class="token function">toUpperCase</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// 练习1：获取员工姓名长度大于3的员工的姓名。</span>
        <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employees <span class="token operator">=</span> <span class="token class-name">EmployeeData</span><span class="token punctuation">.</span><span class="token function">getEmployees</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">></span></span> nameStream <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">Employee</span><span class="token operator">::</span><span class="token function">getName</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        nameStream<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>name <span class="token operator">-></span> name<span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// 练习2：</span>
        <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Stream</span><span class="token punctuation">&lt;</span><span class="token class-name">Character</span><span class="token punctuation">></span><span class="token punctuation">></span></span> streamStream <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">StreamAPITest</span><span class="token operator">::</span><span class="token function">fromStringToStream</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        streamStream<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span>s <span class="token operator">-></span><span class="token punctuation">&#123;</span>s<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">&#125;</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//两层遍历</span>

        <span class="token comment">// flatMap(Function f) —— 接收一个函数作为参数，将流中的每个值都换成另一个流，然后把所有流连接成一个流。</span>
        <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Character</span><span class="token punctuation">></span></span> characterStream <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">flatMap</span><span class="token punctuation">(</span><span class="token class-name">StreamAPITest</span><span class="token operator">::</span><span class="token function">fromStringToStream</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        characterStream<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//一层遍历</span>
    <span class="token punctuation">&#125;</span>

    <span class="token comment">//将字符串中的多个字符构成的集合转换为对应的Stream的实例</span>
    <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Character</span><span class="token punctuation">></span></span> <span class="token function">fromStringToStream</span><span class="token punctuation">(</span><span class="token class-name">String</span> str<span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Character</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token class-name">Character</span> c <span class="token operator">:</span> str<span class="token punctuation">.</span><span class="token function">toCharArray</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
            list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span>c<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">&#125;</span>
        <span class="token keyword">return</span> list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span></code></pre>


<h4 id="3、排序"><a href="#3、排序" class="headerlink" title="3、排序"></a>3、排序</h4><table>
<thead>
<tr>
<th>方法</th>
<th>描述</th>
</tr>
</thead>
<tbody><tr>
<td><strong>sorted</strong>()</td>
<td>产生一个新流，其中按自然顺序排序</td>
</tr>
<tr>
<td><strong>sorted</strong>(Comparator com)</td>
<td>产生一个新流，其中按比较器顺序排序</td>
</tr>
</tbody></table>
<pre class="language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@Test</span> <span class="token comment">/* 排序 */</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test4</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
    <span class="token comment">// sorted() —— 自然排序</span>
    <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">asList</span><span class="token punctuation">(</span><span class="token number">12</span><span class="token punctuation">,</span> <span class="token number">43</span><span class="token punctuation">,</span> <span class="token number">65</span><span class="token punctuation">,</span> <span class="token number">34</span><span class="token punctuation">,</span> <span class="token number">87</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> <span class="token operator">-</span><span class="token number">98</span><span class="token punctuation">,</span> <span class="token number">7</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">sorted</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token comment">// sorted(Comparator com) —— 定制排序</span>
    <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employees <span class="token operator">=</span> <span class="token class-name">EmployeeData</span><span class="token punctuation">.</span><span class="token function">getEmployees</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">sorted</span><span class="token punctuation">(</span><span class="token punctuation">(</span>e1<span class="token punctuation">,</span> e2<span class="token punctuation">)</span> <span class="token operator">-></span> <span class="token punctuation">&#123;</span>
        <span class="token keyword">int</span> ageValue <span class="token operator">=</span> <span class="token class-name">Integer</span><span class="token punctuation">.</span><span class="token function">compare</span><span class="token punctuation">(</span>e1<span class="token punctuation">.</span><span class="token function">getAge</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> e2<span class="token punctuation">.</span><span class="token function">getAge</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>ageValue <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
            <span class="token keyword">return</span> <span class="token operator">-</span><span class="token class-name">Double</span><span class="token punctuation">.</span><span class="token function">compare</span><span class="token punctuation">(</span>e1<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> e2<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">&#125;</span>
        <span class="token keyword">return</span> ageValue<span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span></code></pre>

<h3 id="五、Stream-的终止操作"><a href="#五、Stream-的终止操作" class="headerlink" title="五、Stream 的终止操作"></a>五、Stream 的终止操作</h3><p>  终端操作会从流的流水线生成结果。其结果可以是任何不是流的值，例如：List、Integer，甚至是 void 。<strong>流进行了终止操作后，不能再次使用</strong>。</p>
<h4 id="1、匹配与查找"><a href="#1、匹配与查找" class="headerlink" title="1、匹配与查找"></a>1、匹配与查找</h4><table>
<thead>
<tr>
<th>方法</th>
<th>描述</th>
</tr>
</thead>
<tbody><tr>
<td><strong>allMatch</strong>(Predicate&lt;T&gt; p)</td>
<td>检查是否匹配所有元素</td>
</tr>
<tr>
<td><strong>anyMatch</strong>(Predicate&lt;T&gt; p)</td>
<td>检查是否至少匹配一个元素</td>
</tr>
<tr>
<td><strong>noneMatch</strong>(Predicate&lt;T&gt; p)</td>
<td>检查是否没有匹配所有元素</td>
</tr>
<tr>
<td><strong>findFirst</strong>()</td>
<td>返回第一个元素</td>
</tr>
<tr>
<td><strong>findAny</strong>()</td>
<td>返回当前流中的任意元素</td>
</tr>
<tr>
<td><strong>count</strong>()</td>
<td>返回流中元素总数</td>
</tr>
<tr>
<td><strong>max</strong>(Comparator&lt;T&gt; c)</td>
<td>返回流中最大值</td>
</tr>
<tr>
<td><strong>min</strong>(Comparator&lt;T&gt; c)</td>
<td>返回流中最小值</td>
</tr>
<tr>
<td><strong>forEach</strong>(Consumer&lt;T&gt; c)</td>
<td><strong>内部迭代</strong>(使用 Collection 接口需要用户去做迭代，称为<strong>外部迭代</strong>。相反，Stream API 使用内部迭代——它帮你把迭代做了) 。当Stream为parallel的时候,它是并行处理多线程的，所以不能保证输出数据的顺序，但是处理数据的效率比较高</td>
</tr>
<tr>
<td><strong>forEachOrdered</strong>(Consumer&lt;T&gt; c)</td>
<td>当Stream 为parallel的时候，虽然是多个线程并行处理的。但是还是会按照他原有的顺序输出的，底层是通过happensbefore原则保证了它的内存可见性</td>
</tr>
</tbody></table>
<h4 id="2、规约"><a href="#2、规约" class="headerlink" title="2、规约"></a>2、规约</h4><table>
<thead>
<tr>
<th>方法</th>
<th>描述</th>
</tr>
</thead>
<tbody><tr>
<td><strong>reduce</strong>(T iden, BinaryOperator&lt;T&gt; b)</td>
<td>可以将流中元素反复结合起来，得到一个值。返回 T</td>
</tr>
<tr>
<td><strong>reduce</strong>(BinaryOperator&lt;T&gt; b)</td>
<td>可以将流中元素反复结合起来，得到一个值。返回 Optional&lt;T&gt;</td>
</tr>
<tr>
<td><strong>reduce</strong>(U iden, BiFunction&lt;U, T, U&gt; f, BinaryOperator&lt;U&gt; b)</td>
<td>可以将流中元素反复结合起来，得到一个值。返回 U</td>
</tr>
</tbody></table>
<h4 id="3、收集"><a href="#3、收集" class="headerlink" title="3、收集"></a>3、收集</h4><table>
<thead>
<tr>
<th>方法</th>
<th>描述</th>
</tr>
</thead>
<tbody><tr>
<td>&lt;R, A&gt; R <strong>collect</strong>(Collector&lt;T, A, R&gt; c)</td>
<td>将流转换为其他形式。接收一个 Collector&lt;T, A, R&gt;接口的实现，用于给Stream中元素做汇总的方法</td>
</tr>
</tbody></table>
<p>  Collector&lt;T, A, R&gt; 接口中方法的实现决定了如何对流执行收集的操作(如收集到 List、Set、Map)。另外， Collectors 实用类提供了很多静态方法，可以方便地创建常见收集器实例，具体方法与实例如下表：</p>
<table>
<thead>
<tr>
<th>方法</th>
<th>最终的收集类型</th>
<th>作用</th>
</tr>
</thead>
<tbody><tr>
<td><strong>toList</strong>()</td>
<td>List&lt;T&gt;</td>
<td>把流中元素收集到List</td>
</tr>
<tr>
<td><strong>toSet</strong>()</td>
<td>Set&lt;T&gt;</td>
<td>把流中的元素收集到Set</td>
</tr>
<tr>
<td><strong>toCollection</strong>(Supplier&lt;C&gt; factory)</td>
<td>Collection&lt;T&gt;</td>
<td>把流中的元素收集到创建的集合</td>
</tr>
<tr>
<td><strong>counting</strong>()</td>
<td>Long</td>
<td>计算流中元素个数</td>
</tr>
<tr>
<td><strong>summingInt</strong>(ToIntFunction&lt;T&gt; mapper)</td>
<td>Integer</td>
<td>返回一个收集器，该收集可以将流中的每个T类型的元素通过ToIntFunction转换成int后，进行求和</td>
</tr>
<tr>
<td><strong>summingLong</strong>(ToLongFunction&lt;T&gt; mapper)</td>
<td>Long</td>
<td>返回一个收集器，该收集可以将流中的每个T类型的元素通过ToLongFunction转换成long后，进行求和</td>
</tr>
<tr>
<td><strong>summingDouble</strong>(ToDoubleFunction&lt;T&gt; mapper)</td>
<td>Double</td>
<td>返回一个收集器，该收集可以将流中的每个T类型的元素通过ToDoubleFunction&amp;lt转换成double后，进行求和</td>
</tr>
<tr>
<td><strong>averagingInt</strong>(ToIntFunction&lt;T&gt; mapper)</td>
<td>Integer</td>
<td>返回一个收集器，该收集可以将流中的每个T类型的元素通过ToIntFunction转换成int后，求取转换后元素的算术平均值</td>
</tr>
<tr>
<td><strong>averagingLongt</strong>(ToLongFunction&lt;T&gt; mapper)</td>
<td>Long</td>
<td>返回一个收集器，该收集可以将流中的每个T类型的元素通过ToLongFunction转换成long后，求取转换后元素的算术平均值</td>
</tr>
<tr>
<td><strong>averagingDoublet</strong>(ToDoubleFunction&lt;T&gt; mapper)</td>
<td>Double</td>
<td>返回一个收集器，该收集可以将流中的每个T类型的元素通过ToDoubleFunction转换成double后，求取转换后元素的算术平均值</td>
</tr>
<tr>
<td><strong>summarizingInt</strong>(ToIntFunction&lt;T&gt; mapper)</td>
<td>IntSummaryStatistics</td>
<td>该收集器对流中每个T类型的元素应用生成int的映射函数，并返回结果值的汇总统计信息。如：平均值、和、个数、最大值、最小值等</td>
</tr>
<tr>
<td><strong>summarizingLong</strong>(ToLongFunction&lt;T&gt; mapper)</td>
<td>IntSummaryStatistics</td>
<td>该收集器对流中每个T类型的元素应用生成long的映射函数，并返回结果值的汇总统计信息。如：平均值、和、个数、最大值、最小值等</td>
</tr>
<tr>
<td><strong>summarizingDouble</strong>(ToDoubleFunction&lt;T&gt; mapper)</td>
<td>IntSummaryStatistics</td>
<td>该收集器对流中每个T类型的元素应用生成double的映射函数，并返回结果值的汇总统计信息。如：平均值、和、个数、最大值、最小值等</td>
</tr>
<tr>
<td><strong>joining</strong>()</td>
<td>String</td>
<td>连接流中每个字符串</td>
</tr>
<tr>
<td><strong>joining</strong>(CharSequence delimiter)</td>
<td>String</td>
<td>按指定分隔符delimiter，连接流中每个字符串</td>
</tr>
<tr>
<td><strong>joining</strong>(CharSequence delimiter, CharSequence prefix, CharSequence suffix)</td>
<td>String</td>
<td>按指定分隔符delimiter，以及指定前后缀，连接流中每个字符串</td>
</tr>
<tr>
<td><strong>maxBy</strong>(Comparator&lt;T&gt; c)</td>
<td>Optional&lt;T&gt;</td>
<td>根据比较器选择最大值</td>
</tr>
<tr>
<td><strong>minBy</strong>(Comparator&lt;T&gt; c)</td>
<td>Optional&lt;T&gt;</td>
<td>根据比较器选择最小值</td>
</tr>
<tr>
<td><strong>reducing</strong>(BinaryOperator&lt;T&gt; op)</td>
<td>Optional&lt;T&gt;</td>
<td>从一个作为累加器的初始值开始，利用BinaryOperator与流中元素逐个结合，从而归约成单个值</td>
</tr>
<tr>
<td><strong>collectingAndThen</strong>(Collector&lt;T,A,R&gt; downstream, Function&lt;R,RR&gt; finisher)</td>
<td>转换函数返回的类型RR</td>
<td>包裹一个收集器，并对其结果进行转换。在收集后执行附加的转换操作</td>
</tr>
<tr>
<td><strong>groupingBy</strong>(Function&lt;T,K&gt; classifier)</td>
<td>Map&lt;K, List&lt;T&gt;&gt;</td>
<td>根据分类函数classifier的返回值进行分组。利用此可以根据某属性值对流分组，属性为K，结果为V</td>
</tr>
<tr>
<td><strong>partitioningBy</strong>(Predicate&lt;T&gt; p)</td>
<td>Map&lt;Boolean, List&lt;T&gt;&gt;</td>
<td>根据true或false进行分区</td>
</tr>
</tbody></table>
<pre class="language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">StreamAPITest</span> <span class="token punctuation">&#123;</span>
    <span class="token comment">/* 1-匹配与查找 */</span>
    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test1</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employees <span class="token operator">=</span> <span class="token class-name">EmployeeData</span><span class="token punctuation">.</span><span class="token function">getEmployees</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// allMatch(Predicate p) —— 检查是否匹配所有元素。</span>
        <span class="token comment">/*练习：是否所有的员工的年龄都大于18*/</span>
        <span class="token keyword">boolean</span> allMatch <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">allMatch</span><span class="token punctuation">(</span>e <span class="token operator">-></span> e<span class="token punctuation">.</span><span class="token function">getAge</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">18</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>allMatch<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// anyMatch(Predicate p) —— 检查是否至少匹配一个元素。</span>
        <span class="token comment">/*练习：是否存在员工的工资大于 10000*/</span>
        <span class="token keyword">boolean</span> anyMatch <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">anyMatch</span><span class="token punctuation">(</span>e <span class="token operator">-></span> e<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">10000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>anyMatch<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// noneMatch(Predicate p) —— 检查是否没有匹配的元素。</span>
        <span class="token comment">/*练习：是否存在员工姓“雷”*/</span>
        <span class="token keyword">boolean</span> noneMatch <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">noneMatch</span><span class="token punctuation">(</span>e <span class="token operator">-></span> e<span class="token punctuation">.</span><span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">startsWith</span><span class="token punctuation">(</span><span class="token string">"雷"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>noneMatch<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// findFirst —— 返回第一个元素</span>
        <span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employee <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">findFirst</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>employee<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// findAny —— 返回当前流中的任意元素</span>
        <span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employee1 <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">parallelStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">findAny</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>employee1<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>

    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test2</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employees <span class="token operator">=</span> <span class="token class-name">EmployeeData</span><span class="token punctuation">.</span><span class="token function">getEmployees</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// count —— 返回流中元素的总个数</span>
        <span class="token keyword">long</span> count <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>e <span class="token operator">-></span> e<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">5000</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">count</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>count<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// max(Comparator c) —— 返回流中最大值</span>
        <span class="token comment">/*练习：返回最高的工资：*/</span>
        <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Double</span><span class="token punctuation">></span></span> salaryStream <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span>e <span class="token operator">-></span> e<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Double</span><span class="token punctuation">></span></span> maxSalary <span class="token operator">=</span> salaryStream<span class="token punctuation">.</span><span class="token function">max</span><span class="token punctuation">(</span><span class="token class-name">Double</span><span class="token operator">::</span><span class="token function">compare</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>maxSalary<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// min(Comparator c) —— 返回流中最小值</span>
        <span class="token comment">/*练习：返回最低工资的员工*/</span>
        <span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employee <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">min</span><span class="token punctuation">(</span><span class="token punctuation">(</span>e1<span class="token punctuation">,</span> e2<span class="token punctuation">)</span> <span class="token operator">-></span> <span class="token class-name">Double</span><span class="token punctuation">.</span><span class="token function">compare</span><span class="token punctuation">(</span>e1<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> e2<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>employee<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// forEach(Consumer c) —— 内部迭代</span>
        employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// 使用集合的遍历操作</span>
        employees<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>

    <span class="token comment">/* 2-归约 */</span>
    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test3</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token comment">// reduce(T identity, BinaryOperator op) —— 可以将流中元素反复结合起来，得到一个值。返回 T</span>
        <span class="token comment">/*练习1：计算1-10的自然数的和*/</span>
        <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> list <span class="token operator">=</span> <span class="token class-name">Arrays</span><span class="token punctuation">.</span><span class="token function">asList</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">,</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">,</span><span class="token number">7</span><span class="token punctuation">,</span><span class="token number">8</span><span class="token punctuation">,</span><span class="token number">9</span><span class="token punctuation">,</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">Integer</span> sum <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token class-name">Integer</span><span class="token operator">::</span><span class="token function">sum</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>sum<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// reduce(BinaryOperator op) —— 可以将流中元素反复结合起来，得到一个值。返回 Optional&lt;T></span>
        <span class="token comment">/*练习2：计算公司所有员工工资的总和*/</span>
        <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employees <span class="token operator">=</span> <span class="token class-name">EmployeeData</span><span class="token punctuation">.</span><span class="token function">getEmployees</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">Stream</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Double</span><span class="token punctuation">></span></span> salaryStream <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">Employee</span><span class="token operator">::</span><span class="token function">getSalary</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment">//Optional&lt;Double> sumMoney = salaryStream.reduce(Double::sum);</span>
        <span class="token class-name">Optional</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Double</span><span class="token punctuation">></span></span> sumMoney <span class="token operator">=</span> salaryStream<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">(</span><span class="token punctuation">(</span>d1<span class="token punctuation">,</span> d2<span class="token punctuation">)</span> <span class="token operator">-></span> d1 <span class="token operator">+</span> d2<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>sumMoney<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token punctuation">&#125;</span>

    <span class="token comment">/* 3-收集 */</span>
    <span class="token annotation punctuation">@Test</span>
    <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test4</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">&#123;</span>
        <span class="token comment">// collect(Collector c) —— 将流转换为其他形式。接收一个 Collector接口的实现，用于给Stream中元素做汇总的方法</span>
        <span class="token comment">/*练习1：查找工资大于6000的员工，结果返回为一个List或Set*/</span>
        <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employees <span class="token operator">=</span> <span class="token class-name">EmployeeData</span><span class="token punctuation">.</span><span class="token function">getEmployees</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">List</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employeeList <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>e <span class="token operator">-></span> e<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">6000</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">toList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        employeeList<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token class-name">Set</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Employee</span><span class="token punctuation">></span></span> employeeSet <span class="token operator">=</span> employees<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>e <span class="token operator">-></span> e<span class="token punctuation">.</span><span class="token function">getSalary</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> <span class="token number">6000</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token class-name">Collectors</span><span class="token punctuation">.</span><span class="token function">toSet</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        employeeSet<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token operator">::</span><span class="token function">println</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
<span class="token punctuation">&#125;</span></code></pre>


                
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